The present invention relates to detecting and eliminating conductive irregularities such as conductor breaks in a wire wound ignition wire core, and, more specifically, relates to an apparatus for detecting conductive irregularities such as conductor breaks in wire wound ignition wire during the manufacturing process and to a method utilizing the apparatus for detecting these irregularities and for systematically eliminating them from the manufacturing process prior to the insulation coating being extruded thereover.
Automotive ignition wire has numerous constructions. A number of these constructions have a core consisting of a wire conductor wrapped around a rubber jacketed fiberglass cord and then given a thin coating of a semi-conductive material, over which an insulation is extruded, typically braided and then jacketed and cured.
During the production of this automotive ignition wire, conductive irregularities such as conductor breaks can occur at a number of the various steps in the manufacturing process, especially during the winding of the conductor around the rubber coated fiberglass core and the various coatings placed thereon prior to the insulation coating. This conductive irregularities problem such as conductor breaks has resulted in the rejection of entire shipments of automotive ignition wire by end users and the return thereof to the manufacturer.
In previous efforts to detect and eliminate the conductive irregularity problem, small samples of the ignition wire core were selected at random and then tested for adherence to user specifications. This method proved unacceptable because of the excessive time required and the scrap generated thereby. Additionally since this sampling method was preformed infrequently, it was unable to detect small sporadic irregularities. Since many of the conductive irregularities were small conductor breaks which resulted in relatively small increases in wire resistance due to the semi-conductive coating holding the ends of the broken wire close so that conduction of current across the break occurred, there is a need for an apparatus and a method that will systematically detect and therefore provide for the elimination of conductive irregularities such as small conductive breaks in the overwrapped ignition wire core early in the manufacturing process.
U.S. Pat. No. 3,890,179 to Deardurff provided a continuous monitoring device for measuring the resistance of the filament bundle and then compensated for variances in the conductance between the core and the semi-conductive overcoat by controlling the degree of curing. While this method of insuring uniform conductance between the core and the semi-conductive overcoat apparently worked, it did not appear to provide for the detection of small conductive irregularities such as breaks in the conductor and was most likely ineffective at speeds as high as 300 fpm.
The concept of measuring a resistance in a conductor between two points in production process is known and is illustrated in such patents as U.S. Pat. No. 3,863,148 to Fellrath, issued Jan. 28, 1975; U.S. Pat. No. 3,890,567 to Knufflmann issued June 17, 1979, and U.S. Pat. No. 3,694,736 to Wakefield issued Sept. 26, 1972. It is also known to monitor and check the continuity of an electrically insulated wire to detect breaks in conductors and the insulated wire as disclosed in U.S. Pat. No. 4,241,304 to Clinton issued Dec. 23, 1980.
These various prior art apparatus were apparently unable to satisfactorily detect the conductive irregularities such as fine breaks in the ignition wire core running at processing speeds in excess of 300 fpm, or to automatically stop the manufacturing process to allow for the elimination of the detected conductive irregularities during the manufacturing process.
Accordingly, there is a need for ignition wire core conductive irregularities detector and a method of monitoring the ignition wire core resistant during the ignition wire manufacturing process. The apparatus and the method should be employed early in the manufacturing process and should provide for stopping the manufacturing process to allow for the elimination of the conductive irregularities prior to the insulation coat being applied to the ignition wire core.